Digital micromirror devices (DMDs) are taught in U.S. Pat. No. 5,061,049, "Spatial Light Modulator and Method," assigned to Texas Instruments Incorporated. DMDs are comprised of a very small deflectable structure, typically a mirror, suspended over an air gap. There are several forms of DMDs, each named after the means of supporting the mirror, including cantilever beam, cloverleaf, and torsion beam. The mirror of the torsion beam DMD is supported by two torsion hinges attached to opposing corners of the mirror. A voltage differential between the mirror and two address electrodes located under the mirror causes the mirror to deflect or rotate about the hinge axis until stopped by landing electrodes. When the mirror is deflected, light projected onto the surface of the mirror will be modulated by the deflected mirror.
When a change in mirror position is desired, a series of reset voltage pulses is applied to the mirror to free the minor from the landing electrode. The mirror is again deflected depending on the voltage bias applied to the addressing electrodes and the mirror. The electrostatic forces generated to deflect and reset the DMD mirrors stress the hinges and support structure of the DMD and can lead to the collapse of the support structure and premature wearout of the hinges. A need exists for a reset method that is capable of freeing stuck mirrors yet does not over stress the DMD hinges or induce any visual artifacts.